The present invention relates to a camshaft driving arrangement for a double overhead camshaft (hereinafter referred as to DOHC) engine.
JP 57-83617 discloses a conventional camshaft driving arrangement for a DOHC engine as shown in FIG. 6.
Referring to FIG. 6, a crankshaft 45 is rotatably mounted to a cylinder block 44, whereas two camshafts 42, 43 are rotatably mounted to a cylinder head 41 disposed on the cylinder block 44. A crank sprocket 46, and two cam sprockets 47, 48 are coupled with the crankshaft 45, and the camshafts 42, 43, respectively. Torque is transmitted from the crankshaft 45 to the two camshafts 42, 43 by means of a rubber timing belt 49.
For recirculating an engine coolant, a water pump (not shown) is disposed on a front wall of the cylinder block 44, and includes a pump shaft 51. Coupled with the pump shaft 51 is a pump sprocket 52 with which the timing belt 49 is in engagement. Thus, torque is transmitted to the water pump from the timing belt 49 through the pump sprocket 52.
The timing belt 49 circulates in a direction as indicated by arrows in FIG. 6, and it is pressed, by a movable tensioner roller 53, on a loose side thereof 49b which is positioned between the crank sprocket 46 and the cam sprocket 47.
A problem encountered in such conventional camshaft driving arrangement is that, since the pump sprocket 52 is in engagement with the timing belt 49 on a tension side 49a theareof, the cylinder block 44 should be increased in width for arranging the water pump, resulting in enlarged dimension and increased weight of the engine.